my routine could be set by clock-work

shorthaul: music during boarding. surf web on phone while seated. fall asleep by taxiing. wake up at cruising, read phone-kindle until landing.

longhaul: music during boarding. newspaper while seated. exact same champagne-champagne-wine-port-coffee sequence during IFE movie. 2 or 3 tv episodes on my laptop. conk out.

i always print some work documents to scan on the plane but that never ever ever comes to realization.

+1
The vast majority of my flights are in Y and sleep is totally out of the question, day or night.
Short haul is fine. I just eat and read.
On a long haul I will watch a movie or two, simply to pass the time. In between I alternate between eating and standing at the back of the cabin (to give my back and rear end a break from the discomfort).
Another favourite activity is staring at the flight map thinking "let me out of this (expletive deleted) metal tube and give me back my life".
It may be an unpopular view on FT, but my trips are all about the destination. The flight itself is simply a means to an end, a way to get from A to B.
I don't bother upgrading because:
1. I'm still stuck on a plane.
2. I still can't sleep. Even in J or F, it's still full of people coughing, snoring and farting (kind of a very expensive hostel dorm).
3. It still takes as long. Get me from ZRH to MEL in 3 hours and I will pay you insane money.
4. I still can't have what I want more than any fine wine or caviar - a Marlboro red!

Depends on the time, distance, amount/urgency of work, my physical state. Activities include: work, reading, watching movies, sleeping, eating, chatting with my neighbor (rare), staring out the window, listening to music or podcasts.

Marvel at the beauty of flight, eat/drink, read a magazine/book, watch a movie/TV show, or work on my laptop.

Read, sleep, listen to music, watch movies/TV, meditate.

I also have a little beauty routine just for when I am airborne.

I am usually a leisure traveller and do not have to work while on long haul flights yet I have a lot of compassion for those who do-kudos to all of you. I could not do that on a regular basis and would love to know your secrets for long distance travel.
I try to plan my travel in Business or First on FF miles usually.
Not with standing, I try my best to only sleep on redeye flights departing the US after 9pm-will eat dinner before and put the bed as flat as I can after takeoff.
Westbound back to the US-usually a good book and some movies.

On the plane, my usual habit has been to read or sleep, regardless of whether I'm travelling for business or leisure. I do find that some of the travel time when it's difficult to read or sleep (e.g., travelling to/from airport, lining up for security, etc) is a good time to brain storm for work.

Lately, I've used fairly long flights as a time to review and tag photos in Lightroom. (In my spare time, I'm a photography student and volunteer photographer for some animal rescue groups, so I have a lot of photos to handle.) I review images, add metadata, name them, etc. It's semi-mindless but really useful to do, and a flight is a good time to do it.

If I absolutely have to do some "day job" work on a plane or lounge, I can fairly passive tasks like read reports, proofread drafts or input data into Excel. But I can't do anything that requires concentrated thought (like drafting a memo).

It might just be me but my level of interest in anything and attention span become drastically short when I'm flying. It doesn't matter if it's working, eating, drinking, watching movies, reading, anything will become boring in 15 minutes.

I no longer travel for work, so it's all about me. Unfortunately, I've never been able to sleep much on a plane (generally falling asleep around 30 minutes before arrival on short haul flights, and only intermittently on long haul, whether in J or Y). So it's usually a mixture of listening to all the baroque, classical, and then country music on the IFE while showing the map, flipping through the movies and TV shows and maybe watching one episode of something or other, reading the newspaper, playing games on my cellphone, eating (business or long haul), drinking (champagne in J long haul, beer in Y long haul, tea and water on all flights), reading the in flight magazine, and getting books and magazines out from my carry-on to read.

And spending 1/2 hour settling down to sleep for 5 minutes, multiple times on a long haul.

And queuing for the washroom.

Most of my flights are business trips, but I do not work on the plane...

I try always to read a magazine or two, listen to some music and sleep during those 10+ hours flights...

I try to tidy up my personal to do list which is a never ending, but not related to work!

besides try to enjoy the drinks I will not drink if I was not in the plane (different region wine mainly).

Years ago, I started picking up a magazine at the airport to read on the plane. Usually Car & Driver, or something like that. Then one time I had a real early flight, and the newsstands weren't open yet! So now I make a stop a day or two ahead of time to get one at the store.

I alternate between my magazine and looking out the window, if the skies are clear. I'm better than almost everyone at identifying where we are. Its one of my few real talents.

Love the responses of those who apparently sit in wonder at human flight. Smirking me wonders if they just sit there, glazed and amazed, peering out the window. But...I'm actually there, too. 747 Pilot Mark Vanhoenacker's book ("Skyfaring") is a nice devotional for this frame of mind, too.

Long haul in Y means carving up the hours into chunks: read, listen to music, write/TV, nap, take a walk. Intersperse with snacks or drinks as desired.

I read British GQ (I always go to the same stand in Calgary where 99% of my travel originates). I will have a bottle of juice, remove my suit coat, make myself as comfortable as one can be on Westjet E+ and basically veg out. If I can't sleep (I can't sleep on the redeye) I'll skim through the IFE and sit there, comatose. If somebody says something to me, I respond, but unless the seatmate is engaging me in conversation - which I strongly welcome - or the FA is asking me to do something, I don't have a care in the world. I try not to worry about anything.

As for when it's time to land, I wake up, place my seat upright, slowly realize where I am, get oriented as to where I'm going and fight my way off the plane.

Typically on landing, I go have a can of Red Bull. Then I (used to) would go for a cigar, but now I opt to just use the airport washroom and proceed to get my luggage.

I almost always travel with checked baggage unless I'm on a puddle jumper to somewhere from a smaller airport. I do not consider my time so valuable that I can't wait for luggage on arrival.

Chuck